贵州独山下泥盆统丹林组陆相地层中的U形潜穴   总被引：2，自引：0，他引：2  

王约 《地质学报》2005,79(1):1-6

具蹼状构造的垂直 U形潜穴 Diplocraterion广泛产出于全球寒武纪—古近纪的滨浅海相中 ,被认为是 Seilacher(196 4 ,196 7)的 Skolithos遗迹相的主要分子 ,也见于中—新生代的河湖相中 ,被视为高能环境的重要分子。Diplocraterion在古生代陆相地层中的发现仍是首次。产于贵州独山丹林组陆相地层具有水平层理的黑色泥岩中的 Diplocraterion dushanensis ichnosp.nov.其近于平行的 U形栖管由许多的节管组成 ,节管和蹼状构造可能系造迹生物的居住潜穴阶段性地随沉积物的增厚而向上移动的过程中所形成 ,其造迹生物主要生活于泛滥平原相对平静贫氧的水体环境中。  相似文献   

新疆柯坪地区寒武纪-奥陶纪碳酸盐岩沉积旋回的碳氧同位素研究   总被引：6，自引：0，他引：6  

谢小敏  胡文瑄  王小林  钱一雄  张军涛  曹剑  李庆 《地球化学》2009,38(1)

野外观测发现,在新疆柯坪地区蓬莱坝剖面,中寒武统阿瓦塔格组(C2a)至下奥陶统蓬莱坝组(O1p)的碳酸盐岩在剖面上存在不同尺度的沉积旋回:体系域级、米级旋回级、藻纹层级.对49件样品进行微区取样,共得到98件样品,对其进行了精细的不同尺度沉积旋回碳氧同位素组成的分析研究.结果表明,碳酸盐岩样品的δ13C值(PDB)分布在-1.6‰～1.6‰之间,平均为-0.5‰,δ18O值(PDB)为-12.7‰～-4.3‰,平均-6.2‰,因此,除了明显受到后期成岩蚀变作用(退白云岩化)的藻碳酸盐岩外,其余样品的碳氧同位素组成总体位于正常的海相碳酸盐岩沉积范围内.在体系域尺度上,对于Ⅲ2旋回层序高水位体系域(C2a1),海平面变化是控制碳酸盐岩碳氧同位素组成的主要因素;对于Ⅲ3旋回层序(C2a2-O1p),伴随海平面的升降变化,岩石沉积微环境复杂多变.在米级旋回尺度上,米级旋回的形成除了受高频海平面变化影响外,还受到古构造、古气候的叠加影响.在藻纹层旋回尺度上,δ13C值比δ18O值更能反映藻纹层的旋回性变化特征,藻纹层的形成受控于有机质沉积速率的季节性变化.  相似文献   

川东北地区飞仙关组层序—岩相古地理特征和鲕滩预测   总被引：4，自引：0，他引：4  

郑荣才  罗平  文其兵  徐发波  李瑜  耿威 《沉积学报》2009,27(1):1-8

以沉积相和界面识别为依据,将川东北地区下三叠统飞仙关组划分为2个三级层序和6个体系域,在此基础上对飞仙关组层序地层学特征进行了分析,编制了各沉积体系域的层序—岩相古地理图和对鲕滩发育规律进行预测。结果表明:SQ1层序发育期,飞仙关组受持续海侵影响,形成以深水台盆为中心的台盆—台地边缘—开阔—局限—蒸发台地的相带展布格局,以海侵体系域的台地边缘和台内鲕滩最为发育,该体系域也是飞仙关组鲕滩相储层最发育的层位;SQ2层序发育期,受海平面大幅度下降和水循环受限及干旱炎热气候影响,区域沉积格局由开阔台地转化为局限台地,鲕滩逐渐消失,最终进入频繁暴露的蒸发台地环境,以沉积膏云岩为主,为飞仙关组天然气藏极其重要的第一套区域性致密盖层发育层位。  相似文献   

塔里木盆地台盆区中西部中下奥陶统鹰山组沉积环境研究   总被引：9，自引：1，他引：8  

刘伟  张兴阳  顾家裕 《沉积学报》2009,27(3):435-442

关于鹰山组的等时性,前人已作过论述,在此基础上,通过露头、地震相、地层等厚图和岩心分析等手段,恢复了鹰山组沉积环境,明确了以下几个问题:1)道保湾阶和大湾阶台地边缘相带展布及台地边缘类型,指出台带边缘相带上高能礁滩体分布的不连续性;2)碳酸盐台地台缘滩和台内滩广泛发育,滩体形状多为长条形或椭圆型,其走向多平行于台地边缘;3)台地内部有台内洼地存在,台内洼地周围有颗粒滩和生物丘分布,通常在迎风面为滩体,在背风面为生物丘。台内洼地内的沉积物通常是“深水”的富含有机质的碳酸盐,具有较好的生油条件。  相似文献   

Provenance of the Lower Paleozoic Balcarce Formation (Tandilia System, Buenos Aires Province, Argentina): Implications for paleogeographic reconstructions of SW Gondwana   总被引：3，自引：0，他引：3  

Udo Zimmermann  Luis A. Spalletti 《Sedimentary Geology》2009,219(1-4):7-23

Lower Paleozoic moderately sorted quartz–arenites from the Balcarce Formation deposited in eastern Argentina (Tandilia System) comprise mainly detrital material derived from old upper crustal material. The sources were magmatic, sedimentary, and subordinated felsic metamorphic terranes. High concentrations of tourmaline and Ti-rich heavy minerals, including zircon and nearly euhedral chromite, are common. Trace element concentrations (Nb, Cr) on rutile indicate pelitic and metabasaltic sources, respectively. Major element analyses on chromites indicate a basic volcanic protolith of mid-oceanic ridge origin, which was exposed close to the depositional basin. The delivery of chromite may be associated with convergent tectonics causing the consumption and obduction of oceanic crust during pre-Upper Ordovician times. The oblique/orthogonal collision of the Precordillera Terrane with the western border of the Rio de la Plata Craton, west of the Balcarce Basin or source further to the east from a Lower Palaeozoic extensional basin are possibilities.Geochemical and petrographic data exclude the underlying Precambrian and Cambrian sedimentary rocks as dominant sources, and favour the basement of the Río de La Plata Craton, including Cambrian rift-related granites of South Africa and the Sierras Australes (eastern Argentina), as main suppliers of detritus. Trace element geochemistry of recycled pyroclastic material, associated with the quartz–arenites, also suggests volcanic arc sources. The provenance of the pyroclastic material may either be the Puna–Famatina arc, located in north and central Argentina, or a hypothetical active margin further to the south. These ash layers are equivalent in age to volcanic zircons found in the Devonian Bokkeveld Group in western South Africa.The deposition of a glacial diamictite of Hirnantian age (Sierra del Volcán Diamictite) is interpreted as a member of the Balcarce Formation. Based on the stratigraphic re-location of the glacial diamictite and trace fossils, the Balcarce Formation is considered here to be Ordovician to Silurian in age. The Balcarce Formation can be correlated with similar rocks in South Africa, the Peninsula Formation, and the upper Table Mountain Group (Windhoek and Nardouw subgroups), including the Hirnantian glacial deposit of the Pakhuis Formation.  相似文献   

Origin of Lower Cretaceous (‘Nubian’) sandstones of North‐east Africa and Arabia from detrital zircon U‐Pb SHRIMP dating     

KEREN KOLODNER  DOV AVIGAD  TREVOR RUSSELL IRELAND  ZVI GARFUNKEL 《Sedimentology》2009,56(7):2010-2023

Lower Cretaceous sandstones of the type exposed in Israel, deposited over much of North Africa and Arabia as widespread sandstone sheets, typically are mineralogically and texturally mature. Previous petrographic examinations suggested that the Lower Cretaceous sandstones are at least partly a product of recycling and the present study supports this notion. The results of U‐Pb Sensitive High Resolution Ion Micro‐Probe (SHRIMP) dating of detrital zircons from the Lower Cretaceous section exposed in Israel indicate that they are dominated by detrital zircons of Neoproterozoic age, mainly concentrated in the 0·55 to 0·65 Ga interval, with various amounts of older (pre‐Neoproterozoic) zircons (of 0·95 to 1·10, 1·7 to 2·0 and 2·6 to 2·65 Ga age groups). The overall age signal is similar to detrital zircon age spectra previously obtained from the Cambrian–Ordovician sections of Israel and Jordan. Remarkably, the detrital zircon spectra remained almost unchanged for nearly 400 Myr. Thus, the most probable provenance of the Lower Cretaceous sandstone is the recycling of relatively proximal Palaeozoic sandstone. Since first unroofed from above pan‐African terranes closer to the secession of orogeny, the ensuing siliciclastics were recycled repeatedly throughout the Phanerozoic with little additional basement denudation. The Lower Cretaceous sandstone comprises quartz sand that was first eroded from above pan‐African orogens ca 400 Myr prior to deposition.  相似文献   

The discovery of Isocrinus cf. robustus from the Lias Group (Lower Jurassic) near Dunrobin Castle, Sutherland, Scotland     

Aaron W. Hunter  Neil D.L. Clark 《Proceedings of the Geologists' Association. Geologists' Association》2009,120(1):76-78

A single stem section (pluricolumnal) belonging to a post-Palaeozoic crinoid (sea lily) is reported from a small outcrop of Lower Jurassic Lias Group strata exposed in low cliff near Dunrobin Castle. This is the first Jurassic crinoid recorded from Eastern Scotland and the small fragment has enough diagnostic characters to be assigned to the species Isocrinus cf. robustus; a crinoid found commonly in the Lower Jurassic of England. The Scottish form collected has unusual morphology that is atypical of the genus.  相似文献   

Large-scale Tazhong Ordovician Reef-flat Oil-Gas Field in the Tarim Basin of China   总被引：5，自引：5，他引：0  

ZHOU Xinyuan  WANG Zhaoming  YANG Haijun  ZHANG Lijuan  HAN Jianf  WANG Zhenyu 《《地质学报》英文版》2009,83(1):179-188

The Tazhong reef-flat oil-gas field is the first large-scale Ordovician organic reef type oil-gas field found in China. Its organic reefs were developed in the early Late Ordovician Lianglitag Formation, and are the first large reefs of the coral-stromatoporoid hermatypic community found in China. The organic reefs and platform-margin grain banks constitute a reef-flat complex, mainly consisting of biolithites and grainstones. The biolithites can be classified into the framestone, bafflestone, bindstone etc. The main body of the complex lies around the wells from Tazhong-24 to Tazhong-82, trending northwest, with the thickness from 100 to 300 m, length about 220 km and width 5-10 km. It is a reef-flat lithologic hydrocarbon reservoir, with a very complex hydrocarbon distribution: being a gas condensate reservoir as a whole with local oil reservoirs. The hydrocarbon distribution is controlled by the reef complex, generally located in the upper 100-200 m part of the complex, and largely in a banded shape along the complex. On the profile, the reservoir shows a stratified feature, with an altitude difference of almost 2200 m from southeast to northwest. The petroleum accumulation is controlled by karst reservoir beds and the northeast strike-slip fault belt. The total geologic reserves had reached 297.667 Mt by 2007.  相似文献   

Petrology,geochemistry and U–Pb zircon geochronology of lower crust pyroxenites from northern Apennine (Italy): insights into the post-collisional Variscan evolution     

Maria?Rosaria?RennaEmail author  Riccardo?Tribuzio 《Contributions to Mineralogy and Petrology》2009,157(6):813-835

Spinel pyroxenites occur locally as clasts in polygenic breccias from the Late Cretaceous sedimentary mélanges of the Northern Apennine (Italy). They are of cumulus origin and formed in the deep crust by early precipitation of clinopyroxene and minor olivine and late crystallisation of orthopyroxene, spinel, Ti-pargasite and sulphides. Pyroxenites underwent high-temperature (~850°C) subsolidus re-equilibration and ductile deformation with development of mylonitic bands made of clinopyroxene, orthopyroxene, Ti-pargasite and spinel. U–Pb geochronology on zircons revealed the occurrence of inherited grains of Early Proterozoic to Late Devonian age. The inherited zircons are locally rimmed by recrystallised zircon domains. The oldest rims yield a mean concordia U–Pb age at 306 ± 8 Ma, which is considered to date the emplacement of the pyroxenites, in the framework of the post-Variscan lithospheric extension. The incompatible element compositions of calculated melts in equilibrium with clinopyroxenes from the pyroxenites are characterised by Ba, Nb, LREE and Sr enrichment relative to N-MORB. The depleted Nd isotopic signature of the pyroxenites (initial ε_Nd values of +5.3 to +6.1) may be thus linked to primary magmas produced by low degrees of melting of asthenospheric mantle. In addition, the pyroxenites locally record the infiltration of plagioclase-saturated hydrous melts, most likely evolved through fractional crystallisation and enriched in highly incompatible elements, within the clinopyroxene-dominated crystal mush. A thermal event in Late Permian–Middle Triassic caused the partial resetting of zircon U–Pb system.  相似文献   

长江中下游成矿带铜陵矿集区铜多金属矿床模型   总被引：63，自引：10，他引：53  

毛景文  邵拥军  谢桂青  张建东  陈毓川 《矿床地质》2009,28(2):109-119

通过对长江中下游成矿带的系统考察和对前人资料的阅读和研究,聚焦铜陵矿集区,初步提出了一个可以涵盖不同类型矿床的矿床模型.该模型表达为:在早白垩世高钾钙碱性花岗岩侵位过程中,通过岩浆的分馏演化,在岩体隆起部位及其内外接触带形成斑岩-矽卡岩型矿床,由于广泛发育石炭纪至三叠纪碳酸盐岩.钙质和镁质矽卡岩型矿床是最主要的矿床类型.作为斑岩-矽卡岩型矿床系统的一部分,在斑岩-矽卡岩铜金钼矿床外围分布有矽卡岩铜金矿床、脉状金矿床以及脉状铅锌银矿床.长江中下游地区在三叠纪曾作为大别-苏鲁造山带的前陆盆地,在后碰撞时期出现了大量滑覆构造和扩容空间,它们在不整合界面处十分发育.因此,在成矿过程中不仅形成了像新桥那样的厚大矿体,而且在位于不整合界面附近的矽卡岩往往退化蚀变成为具有典型层纹状和曲卷状构造的退化蚀变岩和矿石,甚至沿一些层位交代形成了层控矽卡岩型或Manto型矿体.此外,还提出了运用该模型开展勘查评价的建议.  相似文献